The present invention relates to a temperature compensation circuit and a synthesizer using the temperature compensation circuit, and more particularly to a temperature compensation circuit capable of adjusting a capacitance according to ambient temperature and a related synthesizer.
In a voltage-controlled oscillator (VCO), the oscillating output signal is controlled by a control voltage, wherein the control voltage is inputted to a voltage-controlled capacitor in the VCO to control the capacitance of the voltage-controlled capacitor. However, the voltage-controlled capacitor, inductor and some parasitic capacitor of VCO may further be affected by temperature. In other words, when the control voltage of the VCO is invariant but the ambient temperature is variant, the oscillating frequency of the oscillating output signal may also be varied by the ambient temperature. When the VCO is applied in a phase-locked loop circuit of a wireless communication system, the imperfect temperature immunity of the VCO may seriously affect the locking performance of the phase-locked loop circuit. Therefore, providing a mechanism to compensate the frequency drifting due to the variation of the voltage-controlled capacitor and inductor in the VCO is a significant concern in this field.